In a silver halide photographic element, a color image is formed when the element is exposed to light and then subjected to color development with a primary aromatic amine developer. Color development results in imagewise reduction of silver halide and production of oxidized developer. Oxidized developer reacts with one or more incorporated dye-forming couplers to form an imagewise distribution of dye.
The image dyes that are formed by a coupler during processing have a tendency to fade over time as a result of exposure to light, heat and humidity. As the image dyes of an element fade, this results in deterioration of the image over time. In addition, since the various image dyes may not fade at the same rate, an apparent change in image color may result. Such change is particularly noticeable in the case of magenta image dye fading.
A variety of dye-forming coupler types have been used in photographic materials. Among the known dye-forming couplers are cyclic azoles such as pyrazolotriazoles. These couplers contain bridgehead nitrogen 5,5 fused ring systems and include such couplers as 1H-pyrazolo[5,1-c][1,2,4]triazoles and 1H-pyrazolo[1,5-b][1,2,4]triazoles. These couplers form magenta dyes in response to exposure to green light.
A significant disadvantage of pyrazoloazole couplers is fading of the dyes formed from them by photographic processing due to extended exposure to low levels of light. Compounds which are included in photographic elements to reduce image dye fading are known as light stabilizers. Inclusion of such stabilizers in color photographic materials at a location near to the location of the image dye can reduce the deterioration of the dye images. This is true for dyes formed from pyrazoloazole couplers. U.S. Pat. Nos. 5,236,819 and 5,082,766 and German Published Patent Application OS 4,307,194 describe the use of certain stabilizers with pyrazoloazole couplers to improve their dye stability. The known stabilizers have not been entirely satisfactory in reducing the rate of fading of the image dyes. U.S. Pat. Nos. 5,561,037 and 6,071,686 suggest the use of an aromatic sulfonamide in combination with other specified stabilizers such as cyclic aminosulfones or alkoxyaromatics as useful anti-fade stabilizers for pyrazoloazoles. The aromatic sulfonamides are useful but difficult and expensive to manufacture.
It would be desirable to improve the light stability of image dyes derived from 1H-pyrazolo[1,5-b][1,2,4]triazole dye forming couplers using materials more readily manufactured than the known aromatic sulfonamides, and thereby retain an accurate color rendition of the image for a longer period of time.